Chemistry Reference
In-Depth Information
Fe(CO)
5
,
h
ν
or
(OC)
4
Fe
Fe
2
(CO)
9
,
Δ
MeO
2
C
CO
2
M
e
CO
2
Me
CO
2
Me
6.295
O
Me
MeO
2
C
Fe(CO)
4
MeO
2
C
CO, MeI
MeO
2
C
CO
2
Me
MeO
2
C
CO
2
Me
6.296
6.297
Scheme 6.113
O
C
OC
CO
Fe
Fe
Cp
Cp
C
O
6.298
H BF
4
Fp
Br
Na(Hg)
Fp
6.300
6.301
CpFe(CO)
2
O
OH
HBF
4
OH
2
R
6.299
= Fp
Fp
Fp
R
R
6.302
6.303
Fp
R
6.304
Scheme 6.114
iron carbonyl derivatives, and are often crystalline. Being cationic, they are also much more reactive towards
nucleophiles. An extra synthetic convenience is that they can be made in a variety of ways. The chemistry is
necessarily stoichiometric - this is because the
1
-complex products tend to be very stable. Fp complexes can
be made in several ways. Two of the ways to make them take advantage of the nucleophilicity of the Fp anion
(Scheme 6.114). The Fp
−
anion
6.299
itself can be prepared by reductive cleavage of the Cp
2
Fe
2
(CO)
4
dimer
6.298
with sodium amalgam.
126
Alkylation of Fp
−
with methallyl bromide generates a
1
-allyl complex
6.300
2
-Fp complex
6.301
on treatment with a strong acid with a noncoordinating counter
ion. Alternatively, the anion can be used to open an epoxide. Treatment of the resulting ferri-alcohol
6.302
with acid results in the loss of water and formation of the Fp complex
6.304
.
Another way to make Fp complexes is by exchange (Scheme 6.115), either of bromide with the iron
complex
6.305
with Lewis-acid assistance, or of an alkene from a pre-formed Fp complex. A volatile alkene,
such as isobutene, is a good choice in the second method, as its evaporation from the reaction mixture will
drive the equilibrium in the desired direction.
Although they are drawn as alkenes, the Fp complexes no longer show typical alkene reactivity, being
inert to reactions such as catalytic hydrogenation and electrophilic attack. Instead they are susceptible to
that is converted to a
